Promotional letter for a salon

We received the following email looking for PR advice:

Hi louise,

I have recently started managing a salon that has been open for 3 years, due to staff changes an previous lack of monitoring the salon has lost a lot of clients. (the salon uses isalon, and i have started using it as a resource for information and marketing)

I have done a lot of customer service training as well as various outside technical courses since i took over and am planning on sending a letter with a voucher attached (i.e.: £10 off cbd..etc) and clients get a second and third voucher once attending the salon after each successive visit.

However i am having trouble wording the letter, i would be grateful for any advice you could give.

Kind regards

Kathryn